There are various known tools and instruments for removing biological tissue samples from the body. For example, biopsy needles and punches are used when a small tissue specimen is required for examination, for example, to identify certain medical conditions. Another example of the biological tissue which is often desired to be removed or harvested is a hair follicle. Hair transplantation procedures are well-known, and typically involve harvesting donor hair grafts from the “donor areas,” for example, side and back fringe areas of the patient's scalp, and implanting them in a bald area (“recipient area”). Historically, the harvested hair grafts were relatively large (3-5 mm), although more recently the donor grafts may be single “follicular units,” which are naturally occurring aggregates of 1-3 (and much less commonly, 4-5) closely spaced hair follicles that are distributed randomly over the surface of the scalp. In one well-known process, a linear portion of the scalp is removed from a donor area by dissection, using a scalpel to cut down into the fatty subcutaneous tissue. The strip is then dissected (under a microscope) into the component follicular units, which are then implanted into a recipient area in respective puncture incisions made by a needle or razor blade. Forceps are typically used to grasp and place the follicular unit grafts into the needle puncture locations, although other instruments and methods are known for doing so.
In “Androgenetic Alopecia” (Springer 1996), M. Inaba & Y. Inaba disclose and describe a method for harvesting singular follicular units utilizing a hollow needle punch having a cutting edge and an interior lumen with a diameter of 1 mm, which is about equal to the diameter of critical anatomical parts of a follicular unit. The needle punch is axially aligned with an axis of a follicular unit to be extracted and then advanced into the scalp to cut the scalp about the circumference of the selected follicular unit. Thereafter, the follicular units are easily removed, e.g., using forceps, for subsequent implantation into a recipient site with a specially devised insertion needle. Sometimes, the sharp end of the needle punch cuts through, or transects, the hair shaft, rendering the follicular unit less than desirable. At other times, the incident angle at which the hollow punch contacts the skin surface causes the punch to stretch the skin and cut a relatively large flap of surrounding tissue along with the hair follicle, which may interfere with a subsequent implant procedure.
U.S. Pat. No. 7,172,604 (Cole) discloses an instrument for the extraction of individual follicular units. Several steps in a process disclosed in Cole for extracting a hair follicle from the skin are shown in FIGS. 1A-1C. FIG. 1 shows a section of skin 20 containing a hair follicle 22 with a hair 24 disposed therein, wherein a tubular harvesting punch 26 contacts the surface of the skin. The punch 26 contacts the skin at an angle with respect to the skin's surface over the location at which the hair 24 emerges from the skin. A sharp end of the punch 26 penetrates the skin and advances to a depth D of between about 0.05-0.5 millimeters. The surgeon then angles the punch 26 to an angle α2, shown in FIG. 1C, along the same axis as the hair growth, and further advances the punch into the dermis to a second depth D2 of 2-7 millimeters.
Published U.S. Patent Application 20050267506 (Harris) discloses a method and apparatus for the extraction of follicular units by first scoring the outer skin layers with a sharp punch, removing the sharp punch, and then inserting a blunt punch into the incision to separate the hair follicular unit from the surrounding tissue and fatty layer to reduce the incidence of hair transection. Another U.S. Pat. No. 6,585,746 (Gildenberg) discloses a hair transplantation system utilizing a robotic system, including a robotic arm and a hair follicle end effector associated with the robotic arm that could be used to harvest hair follicles from the donor area.
To illustrate certain problems associated with the existing devices for removal of the biological tissue specimens, including specifically follicular unit harvesting, FIG. 2A shows the outline of a typical biological unit 30 removed from a body surface by a tubular harvesting cannula (not shown) advanced at an angle to the surface. The cannula generally removes a tissue plug 32, preferably centered in the example shown around a follicular unit having a bulb 34 and shaft 36. However, because the cannula advances into the skin at an angle, an undesirable lateral flap 38 of skin in the direction that the cannula is angled may result. This appendage or flap 38 occurs more often in high-speed punching using a harvesting cannula or needle and low angles of incidence from the body surface, such as between 15-45°. The flap 38 may interfere with movement of the biological unit 30 through the harvesting tool, its removal from the body surface and its retention in the removal tool. Moreover, in case of subsequent implantation of the harvested hair, the existence of the flap 38 interferes with the preference for small and closely spaced incisions at the implantation site. FIG. 2B shows an additional problem associated with the sliding of the cannula before a complete penetration of the skin while being advanced at an angle which results again in the creation of the flap and also in biological unit 30 being transected along the shaft 36. These two problems are typical reasons for discarding harvested biological units 30 used in hair transplantation, and may also be undesirable for biopsy or other applications where specimens of biological tissue need to be taken.
Despite certain advances in improving the tools for harvesting of biological tissue, there remains a need for a more efficient harvesting tool that increases the yield of usable harvested specimens, improves retention of the harvested units in the removal tool and the quality of the obtained specimens.